The lenses of human and animal eyes are subject to damage by physical or other external trauma whether accidental or otherwise and by the formation of cataracts. It has been common practice for many years to surgically remove such damaged lenses. An eye with the lens removed is said to be in the aphakic condition. Subsequent to intracapsular or extracapsular lens extraction, the aphakic eye does not have the ability to focus light with the result that the retina receives only a blurred image. Contact lenses, spectacles or a combination of the two have been used in the past with varying degrees of success to focus the light rays to restore vision. The use of contact lenses and eye glasses to overcome aphakia is subject to the fundamental drawback that such devices are located outside of the eye which results in a shift of the optical center from the natural position within the eye. This results in distortion and/or a change in size of the image. Moreover, eyeglasses cannot restore normal binocular vision if the other natural eye remains and contact lenses must be in continuous use to maintain vision in the aphakic eye.
Cataracts are the most common disorder of the eye and are the second leading cause of blindess in the United States. A cataract is a biochemical change in the structure of the lens of the eye which causes transformation of the normal transparent lens to a cloudy or opaque state. The function of the lens is to focus light rays to form a perfect image on the retina. Cataracts interfere with the focusing of the light rays causing the image to become blurred and eventually leading to blindness if unattended. The opacities caused by cataracts are often not distributed uniformly so that the lens has both opaque and clear areas. Therefore, the degree of loss of vision depends on the size, location and densities of the opacities.
There are several basic types of cataracts including congenital cataracts; traumatic cataracts caused by accidental injury; and most common of all, senile cataracts, most prevalent in the elderly. It is not known why senile cataracts develop and the process may proceed over a period of months or even years before treatment is required. At present, the only successful treatment is surgical excision and replacement of the cataractous lens.
The lens of the human eye contains a hard central nucleus within a cortex. Disruption of the perfectly aligned fibers of the cortex and nucleous causes opacities. Large areas of the cortex and nucleus thus gradually become opaque until the image on the retina is blurred. At this point, the cataract has progressed to a stage where some of the resolving power of the eye is lost due to the damage to the lens.
A cataract is treated by relatively simple surgery under local anesthesia in which the lens material affecting vision is removed. Approximately one half million Americans undergo such surgery every year; this being the most common operative procedure performed by ophthalmic surgeons in the United States.
During the operation, the surgeon views the operation site through a high powered microscope which greatly magnifies the lens of the eye to facilitate the procedure. The eye is kept moist with physiological saline throughout the procedure.
In the past, standard procedure for removing the damaged lens involved first dilating the pupil and then making a half circle incision at the junction of the sclera and the clear cornea. The upper half of the cornea is reflected and the iris is retracted to provide access to the entire lens. The lens was then removed by one of several techniques. For example, the lens may be drawn or eased out through the incision by means of a cup-shaped instrument called an erysiphake. The lens may also be removed by a cryoadhesion (freezing) technique known in the art. Such procedures are known as intracapsular techniques, since the lens capsule remains intact.
Another method is to excise the anterior capsule, shell out the nucleus, and vacuum out the cortex. This is an extracapsular technique.
Regardless of the technique of removing the lens, the incision must be large enough for this purpose and must be sutured to complete the operation. The patient requires from about 48 hours to one week to convalesce from such operations due to the discomfort and irritation caused by the large incision.
In recent years intraocular lenses have been developed for implantation in the eye after the cataractous or otherwise damaged lens has been removed, thereby eliminating the need for contact lenses or eyeglasses after surgery.
The first intraocular lens was implanted in a human eye in 1949. From its inception, the intraocular lens has had a tumultuous history. The controversy has centered around the placement, location, design and surface quality of the artificial lenses.